There are many scientific and engineering activities which require highly detailed and precise information concerning specific materials. These include: fabrication of novel microelectronic and photonic device materials designed on the atomic scale; rapid solidification of metals to obtain unusual strength, ductility and corrosion resistance; and production of improved ceramics and composite materials which typically are highly vulnerable to thermal and mechanical problems during processing.
In these and other comparable activities, it is often essential to examine a specimen of a selected material at very high resolution, e.g. to detect lines of less than 1 micrometer width and/or to resolve lines as little as 1.2 micrometer apart. Such high resolution requires advances in the state of the art of x-ray imaging, as practiced in the techniques of radiography, tomography, and diffraction topography. Also, in many applications, including microcardiography and high resolution tomography, it is highly desirable to obtain three-dimensional imaging of the specimens.
In fact, x-ray microtomography is a rapidly developing field for the detection of flaws and defects inside materials produced for industrial applications. For example, the structure of all materials as they are formed is often locally non-uniform over regions of the order of 1 micrometer. Inhomogeneities occurring in diffusion layers and grain boundaries, local compositional variations, regionally homogeneous strains (residual stresses) and inhomogeneous strains, etc., often alter the behavior of materials from their originally designed characteristics.
Successful fabrication of tailored materials having structures not found in nature depends entirely on minute structural details and their influence on the properties and performance of the object fabricated therefrom. Similarly, in microelectronic devices, where different atoms are doped in mutually coherent layers, the thickness and shape of doped layers may change and may cause degradation of functional properties intended to be obtained by the designer. What is needed in such instances is a measurement technique to "see" what happens locally, and to pinpoint local events of significance with high spatial resolution. It is to such needs that the present invention is directed. The invention magnifies, in one or two dimensions, parallel projection monochromatic x-ray images. Such images are obtained, for example, by the techniques of radiography, tomography, and diffraction topography, when the specimen is irradiated with well collimated monochromatic x-rays.
It should be understood that other materials, such as tissue samples from living beings and plants, also may be studied advantageously by high resolution viewing and adequate magnification to clarify significant details, e.g., the presence of abnormal cells or the like.
What is needed, therefore, are apparatus and methods for significantly magnifying a view that is originally generated by the passage of short wave-length hard x-rays through a thin specimen of a selected material. For certain applications, using the same apparatus and method with obvious changes, the x-rays are reflected off a selected surface of a specimen to study its local topography with very high resolution. It is to such needs that the present invention is directed. The invention magnifies, in one or two dimensions, parallel projection monochromatic x-ray images. Such images are obtained, for example, by the techniques of radiography, tomography, and diffraction topography, when the specimen is irradiated with well collimated monochromatic x-rays.
A paper titled "Improvement of Spatial Resolution of Monochromatic X-ray CT Using Synchrotron Radiation" by Sakamoto et al., Japanese Journal of Applied Physics, Volume 27, No. 1, January 1988, pp. 127-132, discloses an x-ray computer tomography technique using synchrotron radiation (SR) as an x-ray source to generate CT images of improved quality. A method is disclosed for improving the spatial resolution, involving the one-dimensional magnification of projection images using asymmetric diffraction. The disclosed method employs a scintillator covering the detector surface. The best spatial resolution obtained was about 15 to 20 micrometers, using a magnification factor of 9.0. The dispersal of visible light, generated by x-rays, in the scintillator appeared to degrade significantly the spatial resolution, as stated on page 130 of the same paper.
There are numerous devices and systems known and commercially available for generating magnified images of very fine details in material samples.
U.S. Pat. No. 4,672,651, to Horiba et al., discloses apparatus and a method in which respective cone-like beams of x-rays are projected from two different directions through a person's body, and the transmitted x-rays are analyzed to generate a projection image. A contrast medium is initially injected into the body to reach a part of the body which is of interest. A direct x-ray detector is used which can also convert a received signal into an optical image which can be directed into a TV camera.
U.S. Pat. No. 4,635,197, to Vinegar et al., discloses a high-resolution tomographic imaging method, wherein a sample is scanned at many points in corresponding cross-sections which are separated by a distance less than the width of an x-ray beam of a CAT scanner. The measured density function thus obtained is deconvolved, with the beam width function for the CAT for each of the plurality of points, to thereby obtain the actual density function for the plurality of points. This information is directly used to generate an image of a sample which has a spatial resolution in the axial direction that is smaller than the width of the x-ray beam of the CAT.
U.S. Pat. No. 5,012,498, to Cuzin et al., discloses an x-ray tomography device which enables the generation of an image at a plane identified transversely through an object. It comprises an x-ray source which supplies high energy pulses which traverse the object. Both the source of the x-rays and the detector are stationary, and the object is rotated.
U.S. Pat. No. Re. 32,779, to Kruger, discloses a radiographic system employing multi-linear arrays of electronic radiation detectors of the CCD type. An x-ray source provides a diverging x-ray beam which passes through portions of a human body to be received first through an image intensifier and then passed through a lens or other focusing device. The transmitted-radiation is focused upon a multi-linear array which comprises a two-dimensional CCD detector.
There clearly exists a need for a high resolution, one-, two- or three-dimensional magnification system and corresponding methods which permit magnifications of up to 200 times the original at resolutions enabling study of features less than 1 micrometer in size and for separation of adjacent features at close to the 1 micrometer level of precision.
The present invention, as described more fully hereinafter, is believed to answer this need. Persons of ordinary skill in the art, upon understanding the present disclosure, are expected to consider obvious modifications of both the apparatus and the method disclosed herein. Such modifications and variations are intended to be comprehended within the scope of the invention described below in detail